The Boeing Company developed "average" winds over nearly every city-pair in the world. Then they established various levels of probability of head or tail wind components over those routes. Hence a 50% probability of a 35 knot headwind, for example, means half of the time the headwind component will be 35 knots or less and half of the time greater than 35 knots. The usual standard for planners and range estimates is 85% probability winds i.e. the headwind will not exceed that component 85% of the time.
I have not been able to find them, I believe Boeing keeps them as proprietary information, selling to others, as fits there desires.
GF